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Sunscreen Products
by Dr Chang Chee Kong, Consultant Dermatologist, Kuala Lumpur

Aspects of photo-protection will be addressed and includes sunscreen products in their various forms, functions, usage and safety profile.

The necessity for photo-protection implies the existence of adverse effects of ultra violet (UV) light which include:

1. hyper-pigmentation
2. acute sunburn inflammation
3. photoaging
4. photocarcinogenesis (induction of skin cancers)
5. phototoxic and photos allergic skin disorders
6. suppression of the skin's immune system
7. cataract formation

Photoaging manifests as a sagging, weather-beaten face with wrinkling, deep furrows, unevenly thickened and thinned skin, white and hyper pigmented spots, proliferation of tiny blood vessels, dehydration, yellowing, skin fragility and inelasticity of the skin.

Photocarcinogenesis on the other hand is the induction of actinic keratosis (premalignant), basal cell carcinoma, squamous cell carcinoma and malignant melanoma. Central to the issue of sun related problems is the fact that 90% of ultraviolet-B rays. (should not have a full stop here) (UVB) is absorbed by the epidermis, of which approximately 70%-80% is blocked by melanin, with the remaining 20% - 30% reaching the dermis.

Thus, in this manner both UVB and UVA rays damage skin cells and the supporting tissue. At the cellular level the outcome will be cell death, as in the sunburn situation, or the induction of abnormal cell lines responsible for skin cancers. In the dermis, on the other hand, UV rays damage both elastin and collagen, which are responsible for the suppleness, support and elasticity of the skin. The outcome of this situation is therefore photo aging.

UV ray penetration of the skin also induces an increased and redistribution of melanin pigment and proliferation of melanin bearing cells.

These facts underscore the importance of effective broad-spectrum photoprotection against both UVB and UVA rays.

Most importantly, it is now current knowledge that these adverse effects can similarly be induced by daily cumulative exposure to low doses of UV rays that often do not produce a sunburn response, a skin signal which, under normal circumstances, would trigger an avoidance response.

Photoprotection as nature's endownment, sets up a first line internal defence system which includes:-

1. scalp hair
2. skin surface lipids
3. urocanic acid secreted in the sweat and which absorbs (UVB) rays
4. stratum corneum (the top layer of skin) which refracts, diffracts and absorbs UVB
5. melanin (skin pigment)
6. beta-carotene (free radical scavengers)
7. antioxidant enzymes
8. DNA repair systems

SUNSCREENS

Excellent photoprotection can be achieved by utilizing modern sunscreens. The ideal sunscreen should filter off the entire spectrum of UV radiation, in particular the hazardous UVB and UVA rays. Additionally, it should adhere properly to the skin i.e. "substantivity", resists heat, perspiration and water, well tolerated, non-greasy and competitively priced.

Most sunscreens are combinations of filters both A) chemical and B) physical.

A) Chemical Filters
These absorb the sun's rays and their specificity of action is defined by their absorption spectrum.

They include:-

I. UVB Filters
a) Para-aminobenzoic acid and derivative
PABA has been gradually phased out in view of allergic reactions that They induce and are superseded by PABA esters e.g. Padimate A Padimate O.

b) Salicylates
These are poor UVB filters but have excellent stability and representedA by octyl and hommomenthyl salicylate.

c) Cinnamates
These are widely used especially Parsol MCX and Cinoxate, and they have the advantage of being insoluble in water thereby providing water resistance.

d) Benzylidene camphor
Widely used as Eusolex 6300.

II. UVB and UVA Filters
Benzophenones are represented by oxybenzone, dioxybenzone and sulfisobenzone.

III. UVA Filters
a) Dibenzoylmethane is represented by excellent UVA filters like Parsol 1789(butyl methoxydibenzoylmethane)
b) Mexoryl SX is a benzylidene camphor derivative.
c) Anthranilates also absorb UVA but their absorption capacity is low.

B) Physical Filters
These are mineral pigments that reflect and scatter UV rays over a broad spectrum of wavelengths that include UVB, UVA, visible light and infra red rays. These are micronised metal salts in the form of titanium and zinc oxide and are usually combined with chemical filters.

Vehicle of sunscreens
Sunscreens are available in several forms namely,

• Emulsions (cream or lotions): Most acceptable photoprotectors. Creams spread easily and offer better photoprotection than lotions. Water-in-oil emulsions gives up more moisture, offers better protection and more water and sweat resist.
• Sticks are excellent sunscreens for lips.
• Gels are unstable and poorly water resistant.

Sun Protection Factor (SPF)
At a certain exposure dose of UVB rays, minimally detectable redness can be observed and is referred to as the minimalerythema dose (MED). The ratio of the MED after application of a photoprotector over the baseline MED i.e. without a photoprotector is referred to as SPF which is thus, an index denoting theefficancy of the particular sunscreen against UVB rays. Thus a sunscreen with an SPF of 2 therefore filters 50% of UVB, an SPF of 15 filters 93.3% of UVB and an SPF of 50 filters 98% of UVB.

However, a rating system for UVA protection is still pending. As such even sunscreens with high SPF ratings need not necessarily render effective photoprotection against UVA.

Choice of sunscreen
Having underscored the importance of broad-spectrum photoprotection, other determinants of choice of sunscreens include:

1. Skin Phototype
Each individual reacts differently to sun exposure and this disparity is denoted by their skin phototype which ranges from Type I to VI, depending on skin, hair and eye ...colour, susceptibility to freckles, sunburn and tanning.

Thus people with fair skin, blue eyes, who burns easily but tans poorly, should use sunscreens with high SPF.

2. Intensity and duration of sun exposure

3. Type of activity may dictate the usage of water and sweat resistant photo protectors. Skiers and mountaineers should be aware that snow reflects UV ray significantly.

4. Latitude
UV exposure is more intense as one gets closer to the equator.

5. Altitude
The quantity of UV received increases at higher altitudes, as the atmospheric layer penetrated by the rays is thinner thus diminishing its filtration effect.

6. Season
UV radiation reaching the earth is more intense in summer than winter.

7. Cloud cover
Clouds completely block infrared radiation, filters almost completely UVB but UVA and visible light penetration remains unimpeded.

8. Glass filters UVB but permits penetration by UVA. Cumulative doses of UVA can therefore be received whilst working behind a window or driving car.

9. Patients on photosensitising drugs and suffering from certain skin disorders will need appropriate photoprotection.

SAFETY PROFILE OF SUNSCREENS
Sunscreens are generally well tolerated and non-toxic. However, allergic reactions can be induced by the fragrance, preservatives, stabilizers or the base.

PABA in chemical filters created a lot of sensitivity problems but their testers seem to be well tolerated albeit with occasional reports of induction of allergic reactions. Other sunscreen chemical filters that have induced allergic reactions are cinnamates, benzylidene camphor, benzophenones, dibenzoylmethanes, and parsol 1789. Maxoryl SX does not induce any adverse effects.

The physical filters do not seem to cause sensitivity problems.

At the present state of knowledge sunscreen are safe for long-term use in children 1 year and above.

Tanning
The tanning ability of an individual is genetically determined and denoted by the skin prototype. In this day and age the sun's rays and UV radiation from artificial sources is considered a tonic. Activities pursued in ernest are sunbathing, outdoor games, and tanning in salons. A deep tan is perceived to portray an aura of health, robustness and beauty. However, the tanned skin is actually damaged skin due to the cumulative adverse effects of UV rays.

The sun worshippers should emulate our wise and fair skinned Oriental maidens who consider the sunrays a toxic agent to be avoided at all cost in their obsessive quest for beauty.

Self-tanning or artificial tanning without the aid of the sun can be achieved by application of a formula containing dihydroxyacetone which when exposed to air produces a brownish yellow colour.